Whether you're avoiding food for political, religious or health reasons, fasting is an excellent exercise in willpower. However, doubts exist about whether fasting is safe for the body. Surprisingly, scientific research shows that fasting for short periods is not especially dangerous and may even have benefits. However, long-term fasting or repeated short fasts can indeed cause harm.
Physical Effects
When a person starts a fast, he usually drops up to a kilogram of weight per day during the first week. This is mostly due to lowered sodium levels in the body. At the same time, the liver produces large amounts of glucose using the available carbohydrates. Fatty acids begin to oxidize, which can increase the liver's sensitivity and potentially cause damage after as little as 72 hours of fasting.
Long-term Fasting
By the third week of a fast, weight loss is down to about 0.3 kg per day. As a fast continues, the body's ketone levels rise and its pH falls. Ketones become the primary energy source for the central nervous system, causing the liver to slow its production of glucose and avoid consuming protein for energy. Insulin levels also fall. As time goes on, a fasting person has increased risk of gout, kidney stones and heart malfunction.
Ramadan
One of the most common occasions for fasting is the holy month of Ramadan, wherein adult Muslims may not eat between sunrise and sunset. Researchers have studied the effects of Ramadan fasting on diabetics and on kidney patients. For kidney patients and Type 2 diabetics, no harmful effects of this fast have been seen as long as the patient has been sure to get enough nutrition each evening. However, Type 1 diabetics may need to take fast-absorption insulin to manage their diabetes throughout the days of fasting.
Intermittent Fasting
Recent research has come to the surprising conclusion that intermittent fasting -- eating only every other day -- may actually improve health. Based on studies showing that dietary restriction increased lifespan for rodents, scientists followed non-obese patients as they fasted every other day. After 22 days, their fat oxidation increased, insulin dropped and glucose levels remained the same. However, subjects felt hungrier than usual throughout the experiment.
Another study attempted to replicate "yo-yo" fasting with mice. The rodents were starved for three days and then fed for four. Scientists found that body weight and fat mass decreased, but potential problems were seen with the subjects' metabolism.
References
- "Western Journal of Medicine"; Fasting: The History, Pathophysiology and Complications; Peter R. Kerndt et al.; November 1982
- "Free Radical Research"; Effects of Fasting on Oxidative Stress in Rat Liver Mitochondria; M. Sorensen et al.; April 2006
- "Transplantation Proceedings"; Impact of Ramadan Fasting on Renal Allograft Function; B. Einollahi et al.; September 2005
- "Diabetes Research and Clinical Practice"; Diabetes and Ramadan: Review of the Literature; B. Benaji et al.; August 2006
- "The American Journal of Clinical Nutrition"; Alternate-day Fasting in Nonobese Subjects: Effects on Body Weight, Body Composition, and Energy Metabolism; Leonie K. Heilbronn et al.; January 2005
- "Nutrition Research and Practice"; Changes in Lipid and Carnitine Concentrations Following Repeated Fasting-Refeeding in Mice; Se Wha Kang et al.; December 2010
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